Rapid developments and applications of communication systems are stimulating new microstructure optoelectronic technologies. Among the various microstructure optoelectronic technologies,integrated optics represents a promising approach. Future electronic systems will require on-chip signal conversion between electrical, optical and microwave media to reach speed and functionality projections. A radically different alternative concept exploits the use of photons, instead of electrons, to carry information in what is commonly referred to as "optical interconnects." One implementation of this strategy relies on the integration of semiconductor- or polymer-based optoelectronic interconnects on a host silicon (Si) substrate, and thus requires feasible semiconductor- or polymer-based optoelectronic technologies in order to produce Si-based photonic devices for optical waveguide interconnects.
Although the technologies for some electro-optic (EO) waveguide devices based on inorganic materials such as crystals and semiconductors have had a long development history, the conditions for manufacturing and processing integrated optical devices are still seriously limited. Thermo-optic (TO) waveguide devices based on polymers and other temperature sensitive materials have shown an exciting potential in low-speed operations because of their flexibility in fabrication and processing. The TO waveguide devices can be built with glass, silica crystal and polymer because only upper modulating electrodes are needed. Especially, polymers not only have higher thermal effects but can also be directly used to fabricate multi-layer integrated optical circuits (IOC) on top of electronic substrate such as Si and Silica. Polymer-based TO waveguide devices have been successfully applied in fiber-optic communications systems and have been receiving more and more attention in this field. A variety of polymer-based new TO waveguide devices aimed at providing feasible structures with enhanced functionability have been reported. Among the active devices in optical communication systems, optical space switches are key components. Large-scale matrix switches are required to meet the increasing switching capacity. Increasing capacity is required as the number of ports increases. A basic switching unit, such as 2.times.2 or 1.times.2 switch, is a suitable unit for building various high capacity switching device.
Wavelength-division-multiplexing (WOM) lightwave systems provide optical communication in wavelength multiplex mode. Recently, research on the devices and techniques for high capability WDM systems or dense wavelength division multiplexing (DWDM) systems having effective network restoration capability, i.e., reconfigurable WDM systems, has received attention. Therefore, single and arrayed high performance optical waveguide switching devices will have wide applications in fiber-optic communication.
Currently, the adding or dropping of signals is accomplished with bulk optics. Individual components such as optical multiplexers, optical demultiplexers, 2.times.2 optical switches, and variable optical attenuators are used to build a programmable optical add/drop network elements. Unfortunately, this solution is costly and labor intensive. By driving integration down to the component level, it is possible to get away from bulk optics with a silicon optical bench. A Si-based array waveguide is used with optical multiplexers and demultiplexers. In this case, optical switching is done with thermo-optic switches. Interconnectivity between rings for provisioning and restoration is also necessary. Today, this function is performed at the electrical level with digital crossconnects at lower bit rates. In the future, it may take place at higher bit rates in the optical layer. In theory, this is possible with optical switching. With such systems, the challenge becomes the provision of reconfiguring an input port to any output port. The bulk optics used today in programmed optical add/drop network elements can serve as prototype systems for reconfigurable optical switches. Since these elements are large and costly to construct, miniaturization is an advantage. Si-based optical-bench technology combined with thermal-optical switches points to the possibility of smaller-scale switches.